1. Field of the Invention
The present invention generally relates to an optical article, especially an ophthalmic lens, having both antistatic and antireflection or reflective properties, which advantageously reduce the attraction of dust on its surface, as well as to a method for making such an optical article.
In particular, the present invention relates to a curable antistatic primer composition having good impact resistant property and good adhesion onto a substrate of the optical article, and its production method
2. Description of Related Art
It is known to protect surfaces of ophthalmic glasses, whether they are mineral or organic, by means of hard coatings (abrasion-resistant and/or scratch-resistant coatings) which are typically based on a polysiloxane.
It is also known to treat ophthalmic lenses, so as to prevent any unwanted reflected light from appearing. The lens is then provided with a mono- or a multilayered antireflective coating, generally made of a mineral material.
When the lens comprises within its structure a hard abrasion-resistant coating, the antireflective coating is generally deposited onto the abrasion-resistant layer surface. Such a stack reduces the impact strength, by rigidifying the system then becoming brittle. This problem is well known in the industry of ophthalmic lenses made of organic glass.
To counteract such a drawback, it has been suggested to provide an impact-resistant primer layer between the lens in organic glass and the abrasion-resistant hard coating.
It is also well known that optical articles made of substantially insulating materials tend to have their surface becoming easily charged with static electricity, particularly when cleaned under dry conditions by rubbing their surface with a wiping cloth, a piece of synthetic foam or of polyester (triboelectricity). Charges present on the surface thereof do create an electrostatic field able of attracting and retaining objects with a very low weight standing in the vicinity (a few centimeters away therefrom), generally very small sized-particles such as dust, and for all the time the charge remains effective on the article.
In order to reduce or to inhibit the particle attraction, it is necessary to reduce the electrostatic field intensity, that is to say to reduce the number of static charges present on the article surface. This may be done by making the charges mobile, for example by inserting a layer of a material inducing a strong mobility of the “charge carriers”, while having good adhesion on substrates, such as organic substrates. The materials inducing the strongest mobility are the so called conducting materials. Thus, a high-conductivity material makes it possible to more rapidly dissipate the charges.
It is also known that even if abrasion-resistant hard coating is applied on the ophtamlic glasses, this hard coat may be scratched when hard dust particles are deposited on the lens surface and is rubbed by the cloth.
The state of the art reveals that an optical article may be given antistatic properties by incorporating into the surface thereof, in the functional coating stack, at least one electroconductive layer, or “antistatic layer”, both expressions being used indifferently.
Such an antistatic layer may form the outer layer of the functional coating stack, or an intermediate layer (inner layer), or may be directly deposited onto the optical article substrate. Incorporating such a layer into a stack provides the article with antistatic properties, even if the antistatic coating is inserted between two not antistatic coatings or substrates.
As used herein, “antistatic” is intended to mean the ability not to retain and/or develop a substantial electrostatic charge. An article is generally considered as having acceptable antistatic properties, when neither attracting nor retaining dust and small particles after one surface thereof has been rubbed using a suitable wiping cloth. It is able to rapidly dissipate the accumulated electrostatic charges, so that such an article seems to be cleaner after having been wiped.
Various methods for quantifying the antistatic properties of a material may be used. For instance, the ability for a glass to drain a static charge off may be quantified by measuring the dissipation time of said charge. Thus, in the present application, a glass is considered as having good antistatic performance if its discharge time is equal to or lower than 500 milliseconds, and preferably around 100-200 milliseconds. Static glasses may possess discharge times of several dozens of seconds and when they have been just wiped may attract surrounding dust during all the time required for their charge to be drained off.
The known antistatic coatings comprise at least one antistatic agent, which is generally a metal oxide (semi)conductor optionally doped, such as indium-tin oxide (ITO), zinc oxide.
Indium-tin oxide (ITO) is the most popular material. It may be indium-doped tin oxide or tin-doped indium oxide. The most commonly used material is typically tin-doped indium oxide, tin being used in an amount of from 5 to 17% by weight.
The applications or patents EP 0834092, DE 3942990, DE 4117257, U.S. Pat. No. 6,852,406, and US 2002/018887 disclose optical articles, especially ophthalmic lenses, provided with an antireflection stack that is mineral in nature comprising a mineral, transparent electrically conductive layer that has been deposited under vacuum, based on titanium dioxide, indium-tin oxide (ITO), zinc oxide, tin oxide, etc. The ITO layer described in the U.S. Pat. No. 6,852,406 has been generally formed from a source comprising 90% indium oxide and 10% tin oxide.
The patent WO 2009/004222, in the name of the applicant, discloses an optical article with antireflection properties, comprising a substrate having at least one main surface coated with an antireflection coating which may comprise at least one electrically conductive layer. This layer preferably comprises a metal oxide selected from indium, tin, zinc oxides and their combinations, the preferred material being indium-tin oxide (ITO).
However, antireflection coatings comprising an ITO-based antistatic layer do not reveal fully satisfying. ITO layers need to be deposited by vacuum deposition in a controlled gas atmosphere. Hence, this solution has the drawbacks of a high cost process (vacuum deposition process) and a lack of flexibility, for instance when the customers want antistatic performance but not antireflection (AR) treatment.
In addition, ITO-based antistatic layers as a drawback suffer from absorbing in the visible range in a not negligle way, so that their thickness must be relatively low, so as to be not detrimental to the transparency properties of the optical article.
To overcome this general issue, polymer electrolytes hybrids have been proposed to form antistatic coating.
In particular, the document US 2012/045577 decribes an antistatic sol/gel primer coating composition comprising:
(a) a hydrolyzate resulting from at least partial hydrolysis of a component A consisting of one or more compounds containing at least one polyalkylene oxide segment and at least one-Si(X)n hydrolyzable group in which n is an integer ranging from 1 to 3, and the X groups independently are precursors of OH groups, such as a silylated polyethylene oxide (silylated PEO); and
(b) at least one inorganic metal salt, such as Li;
wherein component A generates a cross-linked structure upon polymerization of the composition, the dry extract of the composition containing less than 5% by weight free polyalkylene oxide polymers.
So as to form the antistatic primer composition, the silylated polyethylene oxide is hydrolyzed with hydrochloric acid and then a catalyst, a surfactant and lithium salts are added.
The antistatic primer coating made from the above disclosed composition displays good antistatic performances (decay time of arounds 200 ms or less) while having high optical transparency (0% light absorption is achieved).
However, in the system formed by silylated PEO and Li salts, the ionic transport exists mainly in the amorphous phase of the polyethylene oxide (PEO) polymer, whereas the crystalline phase is mostly non-conductive.
In addition, crystallites of silylated PEO matrix induce light scattering, which yields haze on the optical article wherein the antistatic coating sol/gel has been deposited.
Thus, in order to obtain conductive coatings, the crystallization risks should be controlled.
Furthermore, the presence of PEO-Li system in the coatings generally degrades the overall mechanical performances of the optical article, especially hardness (scratch resistance), even if a hard coat is deposited directly onto the antistatic primer layer as compared with standard non-conductive primers.
Moreover, the adhesion of PEO-based primers on certain organic substrates such as MR7®, MR8®, PC (polycarbonate), acrylic lenses of refractive index about 1.6 and high index lenses (such as those materials which have an index of 1.74) can be sometimes lacking.
Other antistatic primer coating composition do not contain PEO. U.S. Pat. No. 6,458,875 describes a poly-urethane-based antistatic coating formed from a composition including polycapolactone (PCL) triol, polycaproloactone diol and bis (4-isocyanato-cyclohexyk)methane. This document teaches to incorporate to this composition 0.5 to 5.0 weight percent of an ionizable salt of a perfluoroalkylsulfonimide, such as lithium trifluoro-methanesulfonimide, to enhance electrical conductivity.
In this document silylated PEO matrix has been replaced by polycaprolactone (PCL) triol and diol. In addition, this document does not mention any reference to the use in ophthalmic articles such as eyeglass lenses.
It should therefore be appreciated that there is a need for improved antistatic primer compositions, especially improved polyurethane antistatic primer compositions, in which the crystallization risks are prevented, while having electrical conductivity without adversely affecting the composition's transparency and or adhesion to an underlying substrate.
In addition, it is still desirable to produce new antistatic primer compositions, which result in antistatic primer coatings that do not impair the optical and mechanical properties of the coated optical article.
Indeed, a unique antistatic primer composition having improved adhesion, mechanical properties and good antistatic properties on all substrate is highly desirable.
In particular, the new antistatic compositions shall provide antistatic primer coatings capable of being themselves coated through a wet coating technique with additional coatings such as an abrasion-resistant and/or scratch resistant coating, while keeping their excellent antistatic properties.
A further goal of the invention is to provide such antistatic primer compositions for forming antistatic and optionally abrasion and/or scratch-resistant layers providing both good adhesion to an optical substrate and/or an additional functional coating formed thereon, and at the same time preserving the optical and mechanical properties of the obtained optical article, for example an ophthalmic lens, (high transmittance, low haze, good abrasion/scratch resistance, good impact resistance) and/or other additional properties such as anti-reflection, anti-smudge, anti-fogging, etc.
Further, soft plastic substrates such as plastic lenses are generally made of soft polymer materials and are easily scratched especially when the lenses are cleaned using a cloth and especially when there are dust deposited on the surfaces. Thus, an antistatic and abrasion and/or scratch resistant primer coating is usually needed for plastic lenses or other soft substrates.